The present invention is in the field of assembly systems for articles made of limp material, and more particularly related to sewing machines.
Sewing machines are well known in the prior art to join portions of a multiple layer limp fabric (or material) workpiece along a curvilinear path, thereby forming a seam. Generally, such systems include a needle adapted for reciprocating motion along a needle axis which is angularly offset from a planar workpiece support surface. The needle is operated in conjunction with an associated bobbin assembly positioned below the workpiece support surface. In most prior art sewing machines, manually or automatically controlled, feed devices present the fabric-to-be-joined is fed to the needle along a feed axis which is fixedly positioned with respect to the needle axis and the workpiece support surface. By way of example, such devices include feed dogs, rolling cylinder feeds and tractor feeds (using endless belts over rollers). U.S. Pat. No. 4,457,243 illustrates a prior art system in which the fabric-to-be-joined is generally advanced toward the needle along a feed axis, while the needle assembly is translatable along an axis transverse to the feed axis to permit a two degree of freedom seam trajectory.
All of such prior art sewing machine systems are very effective in forming straight line seams, but are less effective in providing precision curved seams, as are often required in the assembly of fabric panels to form articles of clothing, for example.
In order to sew a high precision curved seam, during the sewing operation, the fabric-to-be-joined must be presented, or fed, to the needle in the direction of the desired seam. Such a precision curved seam is optimally generated by rotating the fabric-to-be-joined with respect to the sewing head and feed device, or by rotating the sewing head and feed device with respect to the fabric-to-be-joined.
The belts of the sewing machine system of U.S. Pat. No. 4,457,243 can be individually driven to rotate workpiece with respect to a fixed position sewing head and workpiece support surface, prior to or during presentation of the workpiece to the needle. Rotation of the workpiece during sewing is only effective to a limited extent with such systems.
U.S. Pat. No. 4,632,046 illustrates a sewing machine system in which the entire sewing machine head, including the feed device, may be rotated about the needle axis, while maintaining the fabric-to-be-joined in a fixed orientation. Such systems require relatively large and complex assemblies to accomplish these motions.
U.S. Pat. No. 4,512,269 illustrates a prior art seam joining system in which the sewing head, and an associated feed dog assembly, is rotatable about the needle axis, while the remainder of the machine, including the workpiece support surface is maintained stationary.
In the latter-mentioned prior art systems, however, the angle of fabric presentation to the sewing head may be adjusted to establish an improved high precision curved seam compared to the earlier-developed systems, but there is limited near-needle control of the fabric workpiece. Particularly in automated sewing, when workpieces need to be sewn along curvilinear paths, with or without precision easing, the amount of position control of the workpiece near the needle greatly effects the quality of the seam and seam trajectory.
Accordingly, it is an object to provide an improved sewing machine for generating curved or straight seams in a limp fabric workpiece.
It is another object of the present invention to provide an improved sewing machine system having highly accurate near-needle control of the fabric-to-be-joined.
Yet another object is to provide an improved automated sewing machine system for generating curved or straight seams with easing in a limp fabric workpiece.